The invention relates to a method for limiting the speed of a vehicle, a device for carrying out this method and a vehicle having a device of this type.
Devices and methods for automatic speed control in vehicles are known. For instance, there are what are referred to as cruise controls that, when activated, maintain the current speed of the vehicle constantly until the driver intervenes in the driving process by activating the gas pedal or the brake, which leads to deactivation of the cruise control. Furthermore, speed limiters are known in which the driver exerts complete control of the vehicle up to a set speed limiting value and an automatic intervention into the driving characteristics takes place only if the speed approaches the speed limiting value. The intervention is intended to ensure that the predefined speed limiting value is not exceeded and thus to prevent legally prescribed speed limits being undesirably exceeded.
A system of the type just mentioned is known, for example, from DE 1 95 09 492 A1. In said publication, a particular method is applied in which an intervention into the driving characteristics already takes place when the speed approaches the predefined speed limiting value.
In addition, U.S. Pat. No. 6,076,622 discloses a speed limiter in which information from a distance sensor, which detects when the vehicle is approaching another vehicle, is additionally taken into account.
Against this background, the object of the present invention is to make available a vehicle with a speed limiter which is easy and reliable to operate in a variety of driving situations.
This object is achieved by means of a method, a device and a vehicle having the features of the corresponding independent claims. The subclaims contain advantageous refinements.
Firstly, a proposed method for inputting speed limiting values will be explained in detail for the speed limiter of a vehicle. After an activation element is activated by the driver of the vehicle, a current, effective speed limiting value vlim, which depends on the current speed vact of the vehicle, is set.
It is important for the convenience and the reliability of a speed limiting system that the driver can prescribe desired speed limiting values in a simple and intuitive fashion. This objective is achieved with the proposed method because the current speed of the vehicle is taken into account in the evalution of the activation of the activation element. As a result, it is possible to react in a way that is matched to an optimum degree to the input by the driver. This makes the system considerably easier to operate because the settings that are inappropriate for the situation/speed of the vehicle are automatically excluded and the settings that correspond best to the prevailing situation/speed of the vehicle can be adopted with maximum preference. Simplifying the process in which the system is operated in this way serves not only to improve convenience but also safety because because the risk of incorrect settings is reduced and the driver is not distracted from the events on the road by awkward inputting procedures.
The selection of a current speed limiting value vlim after the activation element has been activated can take place, for example, in such a way that, if possible, the next highest predetermined speed limiting value in relation to the current speed vact of the vehicle is selected. Which speed limiting values are predefined for selection depends, in particular, on the respective legal provisions. Thus, in Germany, there is usually a speed limiting value v30=30 km/h for residential areas and a speed limiting value v50=50 km/h for built-up areas. If appropriate, a single speed limiting value can also be predefined for xe2x80x9cselectionxe2x80x9d. In the proposed selection method, that speed limiting value which is closest to the current speed of the vehicle and at the same time higher than it is automatically searched for. In the specified example, given a speed vact of a vehicle of 20 km/h, the limiting value v30 would thus be selected, and given a speed vact of a vehicle of 35 km/h the limiting value v50 would thus be selected. If the speed vact of the vehicle should happen to be above the maximum predefined speed limiting value v50, the proposed selection method cannot be applied. In this case, a suitable alternative selection, for example that of the highest, predefined speed limiting value v50, must be made. An alternative embodiment is explained in more detail below.
The method for selecting a speed limiting value from a predefined set of a plurality of speed limiting values can be developed in such a way that the respective next highest speed limiting value from the series of predefined speed limiting values can be adopted as the current speed limiting value by means of repeated activations of the activation element in close succession. Accordingly, during the first activation of the activation element, a first speed limiting value of the predefined speed limiting values is selected, which can be, as explained, the next highest value in relation to the current speed of the vehicle. However, if the driver does not wish to retain this value, he can cause the next highest of the predefined speed limiting values to be set as the effective speed limiting value by activating the activation key again within a predefined time interval after the first activation. If this speed limiting value is not the desired speed limiting value either, it is possible, by activating the activation key once more, which again must be done within the predefined time interval after the last activation, to make a further jump to the next highest speed limiting value and so on until the desired limiting speed is set.
If the maximum predefined speed limiting value should happen to be reached in the method just explained and if a renewed activation of the activation element should happen to take place within the predefined time interval after the last activation, said renewed activation is preferably interpreted as being a command for deactivation of the speed limiter so that a corresponding signal is generated.
Furthermore, a signal for deactivating the activated speed limiter can be generated if the predefined time interval mentioned above since the last activation of the activation element has expired and the activation element is activated again after that.
The activation element serves, on the one hand, to set a desired speed limiting value and, if appropriate, to activate the speed limiter. On the other hand, it serves simultaneously to deactivate the speed limiter if it is no longer desired. It thus becomes possible for a single activation element to be used for the entire operator control of this limitation process, said element reacting suitably to its activation depending on the situation. This not only provides greater convenience and makes the system easier to operate but also considerably improves the safety. The driver can in fact activate the activation element without looking because it is not a case of selecting one key of several or one specific position setting.
According to one embodiment of the proposed method, after the activation element has been activated, the current speed vact of the vehicle increased by a speed difference xcex94v is set as the current speed limiting value vlim, i.e., vlim=vact+xcex94v. Similarly to a cruise control, the driver can thus set the vehicle to a specific speed and predefine said speed to the automatic system at a guideline value. However, in contrast to a cruise control, no attempt is made to maintain this speed constantly but rather the automatic system merely ensures that the set speed is not exceeded. Such an adoption of a speed of the vehicle as a speed limiting value is possible in combination with the use of predefined speed limiting values as explained above: if the vehicle is at a vehicle speed below the maximum predefined speed limiting value when the activation element is activated, said limiting value or a correspondingly lower speed limiting value can be adopted. On the other hand, if the speed of the vehicle is higher than the highest available predefined speed limiting value, the previously explained method of the adoption of the current speed of the vehicle as a guideline value is applied. In this way, any desired limiting value can be set in an approximated fashion at higher speeds (for example for limiting the speed of the vehicle to 100 km/h on country roads).
The speed difference xcex94v can be treated as a predefined constant. However, it is preferably selected, taking into account the instantaneous acceleration of the vehicle, in such a way that the speed of the vehicle cannot exceed the set speed limiting value vlim until the speed limiter becomes effective. This prevents the situation in which, when the activation element is activated, the current speed of the vehicle which is adopted as the speed limiting value is one which is exceeded just a short time later due to the current acceleration of the vehicle, the upward transgression of the limiting value taking place before the speed limiter can become active and effective. The speed difference xcex94v thus constitutes a safety margin for the functioning of the speed limiter.
According to one embodiment of the method, a signal for reactivating the deactivated speed limiter is generated if the activation element is activated. This means that the switched-off speed limiter is also switched on again by means of the activation element. The activation takes place if the activation element is activated once or if it is activated repeatedly in succession, in which case however there cannot be more than one predefined time interval between individual activations.
Furthermore, a signal for deactivating the activated speed limiter is preferably generated if the vehicle is switched off. This ensures that whenever the vehicle starts, the speed limiter is in the deactivated state.
An input device is also proposed for inputting speed limiting values for a speed limiter of a vehicle. This device has at least one activation element which can be operated by the driver, and a signal input for transmitting a signal which indicates the current speed vact of the vehicle. Furthermore, the input device is configured in such a way that it can carry out a method of the type explained above. After the activation element has been activated, a current speed limiting value vlim, which depends on the current speed vact of the vehicle, is thus set by the input device.
Moreover, a method for limiting the speed of a vehicle is proposed in which, as measures for complying with a predefined speed limiting value vlim, it is preferable to reduce the power of the propulsion unit and/or the torque of the propulsion unit of the vehicle and/or to implement a braking torque if the current speed vact of the vehicle approaches the predefined limiting value vlim or exceeds it. The method is defined in that the aforesaid measures for limiting the speed are temporarily suspended in exceptional situations. On the other hand, after the exceptional situation passes, the measures, and thus the speed limitation, are re-applied if the above preconditions for their activation still apply.
Taking into account exceptional considerably increases the safety of the speed limitation in traffic because in an emergency the driver still has complete control of the vehicle without having to deactivate the speed limiter himself in advance. In exceptional situations, there is in fact no time for such a deactivation initiated by the driver. In addition, such deactivation can easily be forgotten under stressful conditions.
There are various possibilities for the definition of exceptional situations which lead to the speed limiter being suspended. According to a first variant, an exceptional situation occurs if the current speed vact of the vehicle exceeds the instantaneously predefined speed limiting value vlim by more than a predefined speed excess vextra:vact greater than vlim+vextra. Such an exceptional situation can occur if the measures taken by the speed limiter were not able to prevent the predefined speed limiting value vlim from being exceeded. This may be the case, for example, when the vehicle is traveling downhill. As soon as the speed is exceeded in such a way, the measures for limiting the speed are suspended so that the driver is given sole, unaffected control of the vehicle. In this way, it is possible to avoid, for example, skidding when traveling down extreme inclines, which could occur as a result of excessively severe deceleration interventions by the speed limiter.
In the case just explained, the measures for limiting the speed are preferably incrementally reduced as the amount the speed vact of the vehicle exceeds the set speed limiting value vlim is increased. If the speed vact of the vehicle lies above the speed limiting value vlim by the abovementioned speed excess vextra, the measures for limiting the speed are completely switched off. This ensures that the speed limitation is continuously reduced from 100% to 0% in a range of the speed of the vehicle between the predefined speed limiting value vlim and a value which is higher by the speed excess vextra. Conversely, when the speed of the vehicle is decreased, there is a corresponding continuous graduated implementation of the measures for limiting the speed limitation. This ensures that an abrupt transition between the activation and the suspension of the speed limiter, which could adversely affect the driving characteristics of the vehicle, does not take place.
According to another refinement of the method, an exceptional occurs if the position s of the gas pedal and/or the rate ds/dt of the change in position of the gas pedal fulfill a predefined criterion, which points to the request for a high acceleration. Thus, it may, for example, be the case that the driver briefly wishes to effect a maximum acceleration of the vehicle and upward transgression of the predefined speed limiting value during an overtaking procedure or in order to avoid a critical situation. This would not be possible with the speed limiter activated because it would actually attempt to prevent the predefined speed limiting value being exceeded. Accordingly, the driver would have to explicitly deactivate the speed limiter in advance by means of a corresponding operating procedure, which is not only awkward and time-consuming in an emergency situation but is also easily forgotten. For this reason, it is proposed that the observed position and/or rate of the change in position of the gas pedal be taken as a starting point that the driver wishes a maximum acceleration of the vehicle. During detection of such a state, the speed limiter can then be automatically suspended until the criteria for the exceptional situation are no longer fulfilled.
The criterion for the presence of an exceptional situation can consist, for example, in a case when the position s of the gas pedal is beyond a predefined limiting position slim. Thus, an exceptional can be adopted, for example, if the position s of the gas pedal lies between 95% and 100% of the activation travel. In addition, or alternatively, the rate ds/dt of the change in position of the gas pedal can also be used during the detection of an exceptional situation. Here, rapid depression of the gas pedal indicates, through a high rate in the change in position, that a maximum acceleration of the vehicle is expected to be required. Therefore, to detect the exceptional it is not necessary to wait until the gas pedal has been depressed beyond a limiting position.
The activation and/or deactivation of the measures for limiting the speed are/is preferably carried out continuously. In this way, abrupt transitions which could have an adverse effect on the driving characteristics of the vehicle, are avoided.
Furthermore, a control device for limiting the speed of a vehicle is proposed. This device contains an apparatus for reducing the power of the propulsion unit and/or the torque of the propulsion unit and/or for implementing the braking torque. This apparatus is activated if the current speed vact of the vehicle approaches a prescribed speed limiting value vlim or exceeds it. The control device is defined in that it is configured to carry out a method of the type exations the control device temporarily suspends the speed limiting measures. The type of exceptional and their handling can correspond to the variants of the method exlsion unit and an input device for inputting speed limiting values for a speed limiter and having a control device, coupled to the input device, for limiting the speed of the vehicle. The input device and/or the control device can be implemented here as one of the types explained above.
In this vehicle, the input device preferably contains a display which indicates the operating states of the control device to the driver. In particular, it is possible to indicate whether the control device is switched on or off or whether its activity is temporarily suspended owing to an exceptional state. The suspension in the case of an exceptional state is preferably indicated by means of a particularly conspicuous form of indication such as flashing.
The vehicle can have in particular an internal combustion engine and/or an electric motor as its propulsion unit. The use of an electric motor is preferred because it can also be used to implement a braking torque which actively supports the speed limitation in its task of preventing a speed limiting value from being exceeded.